LeBron James and the Cleveland Cavaliers are gargantuan underdogs heading into the NBA Finals

Las Vegas bookmakers don't like the chances of LeBron James and the Cleveland Cavaliers as they get set to take on the Golden State Warriors in the NBA Finals for the fourth consecutive season. Maddie Meyer/Getty Images

LeBron James and the Cleveland Cavaliers are +650 underdogs to upset the Golden State Warriors in the NBA Finals according to Las Vegas bookmakers.

It's the biggest underdog James has ever been in his nine career trips to the NBA Finals.

Game 1 is Thursday, with the Golden State Warriors opening as 12-point favorites over the Cavaliers.

The NBA Finals are officially set, and Las Vegas has the Golden State Warriors heavily favored over the Cleveland Cavaliers to win the seven-game series and take home the NBA Championship for the third time in four years.

The Westgate SuperBook in Las Vegas set the Warriors as -1000 favorites to win the series, meaning bettors would have to put down $1,000 on Golden State to win $100 on their bet. For those that have faith in LeBron James and the underdog Cavaliers, their odds are set at +650, meaning a $100 bet would earn a $650 return should they pull off the upset.

Golden State's enormous odds are the highest any team has had in the NBA Finals in 16 years.

Even in the three previous championship matchups, these two teams have had, the odds have never been this far in one side's favor. The Warriors were just -300 favorites to win the title last year, and the Cavaliers were only +180 underdogs at the start of the series in 2016, which they came back to win after overcoming a 3-1 deficit to stun Golden State.

While it might sound surprising, LeBron is no stranger to playing the role of the underdog. In his nine trips to the Finals, he's been the underdog seven times. That said, the odds indicate that this is looking like James' greatest challenge yet — before this series against the Warriors, the longest odds James had ever faced were +360 in his first Finals appearance against the San Antonio Spurs in 2007.

The NBA Finals tip off this Thursday with Game 1 at Golden State, with the Warriors listed as 12-point favorites to earn the victory in the first game of the series.